1. Field of the Invention
The present invention relates to an optical recording medium and more particularly, to a spare area management method of a rewritable optical recording medium.
2. Discussion of Related Art
An optical storage medium is generally divided into a read only memory (ROM), a write once read many (WORM) memory into which data can be written one time, and rewritable memories into which data can be written several times. Rewritable optical storage mediums, i.e. optical discs, include rewritable compact discs (CD-RW) and rewritable digital versatile discs (DVD-RW, DVD-RAM, DVD+RW).
The operations of writing and playing back data in a rewritable optical disc may be repeated. This repeated process alters the ratio of storage layers for recording data into the optical disc from the initial ratio. Thus, the optical discs lose its characteristics and generate an error during recording/playback. This degradation appears as a defect area at the time of formatting, recording on or playing back from an optical storage medium. Also, defective areas of a rewritable optical disc may be caused by a scratch on its surface, particles of dirt and dust, or errors during manufacture. Therefore, in order to prevent writing into or reading out of the defective area, management of such defective areas is necessary.
FIG. 1 shows a defect management area (DMA) in a lead-in area and a lead-out area of the optical disc to manage a defect area. Particularly, the data area is divided into a plurality of zones for the defect area management, where each zone is further divided into a user area and a spare area. The user area is where data is actually written and the spare area is used when a defect occurs in the user area.
There are four DMAs in one disc, e.g. DVD-RAM, two of which exist in the lead-in area and two exist in the lead-out area. Because managing defective areas is important, the same contents are repeatedly recorded in all four DMAs to protect the data. Each DMA comprises two blocks of 32 sectors, where one block comprises 16 sectors. The first block of the DMA, called a DDS/PDL block, includes a disc definition structure (DDS) and a primary defect list (PDL). The second block of the DMA, called an SDL block, includes a secondary defect list (SDL). The PDL corresponds to a primary defect data storage and the SDL corresponds to a secondary defect data storage.
The PDL generally stores entries of defective sectors caused during the manufacture of the disc or identified when formatting a disc, namely initializing and re-initializing a disc. Each entry is composed of an entry type and a sector number corresponding to a defective sector. The SDL lists defective areas in block units, thereby storing entries of defective blocks occurring after formatting or defective blocks which could not be stored in the PDL during the formatting. Each SDL entry has an area for storing a sector number of the first sector of a block having defective sectors, an area for storing a sector number of the first sector of a block replacing the defective block, and reserved areas. Accordingly, defective areas, i.e. defective sectors or defective blocks, within the data area are replaced with normal or non-defective sectors or blocks by a slipping replacement algorithm and a linear replacement algorithm.
The slipping replacement algorithm is utilized when a defective area is recorded in the PDL. As shown in FIG. 2A, if defective sectors m and n, corresponding to sectors in the user area, are recorded in the PDL, such defective sectors are skipped to the next available sector. By replacing the defective sectors by subsequent sectors, data is written to a normal sector. As a result, the user area into which data is written slips and occupies the spare area in the amount equivalent to the skipped defective sectors. For example, if two defect sectors are registered in the PDL, the user area is slipped into two sectors of the spare area and data may occupy such two sectors of the spare area.
The linear replacement algorithm is utilized when a defective block is recorded in the SDL or when a defective block is found during playback. As shown in FIG. 2B, if defective blocks m and n, corresponding to blocks in either the user or spare area, are recorded on the SDL, such defective blocks are replaced by good blocks in the spare area and the data to be recorded in the defective block are recorded in an assigned spare area.
When replacing defective area with the spare area by utilizing either the slipping or linear replacement, the spare area may become full. If the spare area becomes full, a spare full flag is set to indicate that the spare area is full.
In a disc structure as shown in FIG. 1, a spare full flag exists in each zone and each spare full flag is set according to the status of the corresponding zone, i.e. if the zone is full. Therefore, when the spare area is required for a slipping or linear replacement, the spare full flag is checked to determine if the spare area in the corresponding zone is full, i.e. whether the spare full flag has been set. If the spare full flag has been set, a spare area of a zone in which the spare full flag has not been set is detected and utilized. However, if the spare full flags in all zones have been set, i.e. there is no more spare area, a slipping or linear replacement cannot be executed.
The spare area may be allocated in each zone as described above or may be allocated in a designated portion of the data area. As shown in FIG. 3, the spare area may be allocated on the top portion of the data area. In such case, the spare area is called a Primary Spare Area SA 1. Namely, the data area excluding the primary spare area becomes the user area.
The primary spare area is assigned in an initial formatting process without a logical sector number (LSN).
Thus, the primary spare area is assigned when a manufacturer produces the optical disc or when a user initially formats an empty disc. Also, the size of the primary spare area depends upon the size of the user area. For instance, to have an initial data recording capacity of 4.7 GB, shown in FIG. 3, the primary spare area of 26 MB is assigned. Moreover, when defective sectors are registered in the PDL according to the initial formatting or reformatting of the optical disc, data cannot be recorded in those defective sectors, reducing the recording capacity. Therefore, to maintain the initial data recording capacity, a portion of the primary spare area equivalent to the defective sectors registered on the PDL slips into or becomes a part of the user area during formatting. Accordingly, a physical sector number (PSN) of the user area to which a value of LSN=0 is assigned varies depending upon the defective sectors registered on the PDL.
If the primary spare area becomes full by slipping or linear replacement, as shown in FIG. 4A, a new spare area may be assigned, for example near the end of the user area. Such additional spare area is called a supplementary spare area (SA-2). If the assigned supplementary spare area also becomes full, an extension of the assigned supplementary spare area may be made when necessary as shown in FIG. 4B.
As described above, the assignment of the primary spare is fixed while the supplementary spare area is newly assigned or extendable if necessary. However, in the disc structure as shown in FIGS. 4A and 4B, there is a need to indicate separately whether the primary spare area is full, whether the supplementary spare area has been assigned, or the status of the supplementary spare area as it is extended.